1. Field of the invention
This invention relates in general to well tools used in subsea wells, and in particular to an elastomeric seal which has reinforcing rings.
2. Description of the Prior Art:
In subsea well drilling, operations occur wherein a tool must be lowered through a blowout preventer in a riser, then used to seal against a bore, such as in a subsea wellhead housing. In one instance, it is a good practice to test the blowout preventer by closing the blowout preventer on drill pipe while applying pressure below the drill pipe. The tool at the lower end of the drill pipe seals the bore of the wellhead housing to allow the blowout preventer to be tested. This test also tests the seal of the wellhead connector to the subsea wellhead housing.
In U.S. Pat. No. 5,163,514, Nov. 17, 1992, Charles E. Jennings, an isolation test tool is described for performing the above test. That tools lowers through the blowout preventer and seals in the wellhead housing. The seal is elastomeric, and is set by axial compression.
While workable, frequently, the seal will be pulled off the tool as the tool passes through the blowout preventer stack while the test tool is being retrieved. After pressure is removed from the blowout preventer, the elastomeric portion of the preventer tends to encroach into the riser bore. A combination of mechanical grip, friction, and differential pressure will often stretch and roll the seal out of its groove. This necessitates retrieving the seal from the well. Usually that can be handled by circulation of fluid to float the seal to the surface. However, there is a danger that the seal will catch on downhole structure, making it difficult to retrieve. Also, normally, the seal will be damaged and cannot be reused. Tools other than isolation test tools also have similar problems in retaining elastomeric seals, such as some casing hanger running tools.
It is known to utilize coil springs at the outside corners of the elastomeric seals. These coil springs serve as anti-extrusion members to prevent the seal from extruding axially while set and under test pressure. The coil springs, however, have essentially no circumferential tensile strength so as to avoid interfering with the radial expansion of the seal during energizing. The anti-extrusion rings allow the seal to stretch and be pulled out of its groove upon retrieving of the test tool.